Unsure Which Products to Use on Your Anhydrite Screed Floor?

Anhydrite screed, also known as calcium sulphate, is a very popular floor screed product, due to its high efficiency when paired with a floor heating system. Many underfloor heating engineers recommend anhydrite for this reason.

Tiles are also a popular choice for use with a floor heating system, though anhydrite liquid floor screeding requires primers, adhesives and good preparation for the best final results.

We have put together a list of recommended compatible products that you may want to consider using to ensure compatibility between products at all stages of the flooring process for your floor heating system. First, some useful information for preparing your floor screed ahead of its final finish.

Sanding Down Liquid Floor Screeding After Installation

Anhydrite screed creates a flaky layer called laitance as it thoroughly dries. If you are using a final floor finish which will be fixed to the floor screed’s surface using an adhesive, then you will need to lightly sand the laitance off the surface of the anhydrite screed before using a compatible primer and adhesive.

How to Sand Liquid Screed

This can be done using a universal orbital floor sander with 60 grit sandpaper. Our underfloor heating engineers recommend sanding your screed floor between 7 to 14 days after installation.

Easyflow provides a laitance removal screed sanding service to clients after their liquid floor screeding has been completed. Talk to us for a free consultation and quote for more information.
What should the moisture content of screed be before tiling?

The screed should have a moisture content of 0.5% (or less) weight percent concentration before you lay a tiled floor covering. The moisture content of the screed can be measured using a concrete moisture tester.

If you lay tiles above this level of moisture content, the screed or the adhesive may fail, resulting in tiles coming loose, cracks, or delamination. Easyflow also provides a screed moisture testing service for accurate measurement and timelines for your flooring.

Anhydrite Screed Floor Primers

As of writing, the following floor primers are our recommended products to use ahead of laying your final flooring finish.

Tremco CS175 Epoxy Primer

Water-based epoxy primer for porous substrates. Excellent adhesion to concrete, sand/cement and polymer-modified screeds, including calcium sulphate screeding compounds.

Ball Stopgap P121 Acrylic Primer

Acrylic primer designed to prevent the rapid drying of adhesives and smoothing underlayments to calcium sulphate (anhydrite) screeds.

BAL Prime APD

Rapid-drying acrylic primer for tiling onto plaster walls and plasterboard, anhydrite screed floors and cement floors.

Mapei Primer G

Synthetic-resin-based water-dispersion primer for treating gypsum surfaces prior to fixing ceramic tiles.

Kerakoll Primer A Eco

Water-based surface primer that neutralises the expansive chemical reaction of gypsum or anhydrite based plasters and screeds on contact with cement-based adhesives.

Anhydrite Screed Floor Adhesives

These are our recommended adhesives, some compatible for use with tiled floor heating systems.

Kerakoll H40 Ideal

Professional single-component adhesive suitable for substrates with a gypsum or anhydrite base.

Tilemaster Adhesives AnhyFix

Gypsum based, polymer modified, flexible, rapid setting floor and wall tile adhesive.

Gyptek Adhesive

Gypsum based, flexible floor tile adhesive with high performance rapid setting qualities suitable for application over underfloor heated screeds.

Damp-Proof Epoxy Membranes

These are separate from structural/subfloor damp-proof membranes applied to the subfloor prior to the installation of underfloor heating or screed. We suggest the use of epoxy membranes where structural membranes are missing or damaged. If you are unsure, contact a member of the team.

Laybond Screedmaster One Coat Liquid DPM

Two-part solvent-free epoxy surface damp-proof membrane developed to suppress residual moisture, affording protection for the floor coverings, adhesives, smoothing compounds and primers used in flooring installations.

Tremco Treadfast One Coat Universal

Another two-part epoxy-based surface damp-proof membrane. Suppresses residual constructional moisture in concrete and sand/cement floors.